BHP Billiton is seeing signs that iron ore demand from top consumer China is flattening, raising concerns about Australia's trade outlook, but the world's biggest miner is pushing ahead with its ambitious plans to expand production.

Chinese demand for iron ore has been the driving force behind years of expansion work by the world's biggest mining companies.

More than 100 million rural Chinese are projected to settle in towns and cities in the next decade, requiring unprecedented amounts of steel for housing and infrastructure.

Earlier this month, China cut its 2012 growth target to an eight-year low of 7.5 percent.